examples/c-dataflow/README.md

C Dataflow Example

This examples shows how to create and connect dora operators and custom nodes in C.

Overview

The dataflow.yml defines a simple dataflow graph with the following three nodes:

• node.c is a custom node, i.e., it has its own main function and runs as a separate process. It uses the dora-node-api-c crate to interact with the dora dataflow.
  • The node has a single input named timer that is mapped to a dora-provided periodic timer (dora/timer/secs/1).
  • Whenever the node receives a timer tick, it sends out a message with ID tick and a counter value as data (just a single byte).
  • After receiving 10 timer inputs, the node exits.
• The operator.c file defines a dora operator that is plugged as a shared library into a dora runtime. Instead of defining a main function, it implements a template of dora_* functions, which are invoked by the dora runtime, e.g. when new input is available.
  • The operator takes the tick messages created by the node.c node as input. For each input value, it checks the ID and then prints the received message to stdout.
  • It counts the received values and outputs a string of the format "The current counter value is ...".
• The sink.c file defines a custom node again, which takes the output string of the operator as input. It prints each received input to stdout and exits as soon as the input stream is closed.

Compile and Run

To try it out, you can use the run.rs binary. It performs all required build steps and then starts the dataflow. Use the following command to run it: cargo run --example c-dataflow.

For a manual build, follow these steps:

Build the custom nodes:

• Create a build folder in this directory (i.e., next to the node.c file)
• Compile the dora-node-api-c crate into a static library.
  • Run cargo build -p dora-node-api-c --release
  • The resulting staticlib is then available under ../../target/release/libdora-node-api-c.a.
• Compile the node.c (e.g. using clang) and link the staticlib
  • For example, use the following command:

    clang node.c <FLAGS> -ldora_node_api_c -L ../../target/release --output build/c_node
    

  • The <FLAGS> depend on the operating system and the libraries that the C node uses. The following flags are required for each OS:
    • Linux: -lm -lrt -ldl -pthread
    • macOS: -framework CoreServices -framework Security -l System -l resolv -l pthread -l c -l m
    • Windows:

      -ladvapi32 -luserenv -lkernel32 -lws2_32 -lbcrypt -lncrypt -lschannel -lntdll -liphlpapi
      -lcfgmgr32 -lcredui -lcrypt32 -lcryptnet -lfwpuclnt -lgdi32 -lmsimg32 -lmswsock -lole32
      -lopengl32 -lsecur32 -lshell32 -lsynchronization -luser32 -lwinspool
      -Wl,-nodefaultlib:libcmt -D_DLL -lmsvcrt
      

      Also: On Windows, the output file should have an .exe extension: --output build/c_node.exe
• Repeat the previous step for the sink.c executable

Build the operator:

• Compile the operator.c file into a shared library.
  • For example, use the following commands:

    clang -c operator.c -o build/operator.o -fdeclspec -fPIC
    clang -shared build/operator.o -o build/liboperator.so
    

    Omit the -fPIC argument on Windows. Replace the liboperator.so name with the shared library standard library prefix/extensions used on your OS, e.g. .dll on Windows.

Build the dora coordinator and runtime:

• Build the dora-coordinator executable using cargo build -p dora-coordinator --release
• Build the dora-runtime executable using cargo build -p dora-runtime --release

Run the dataflow:

• Start the dora-coordinator, passing the paths to the dataflow file and the dora-runtime as arguments:

  ../../target/release/dora-daemon --run-dataflow dataflow.yml ../../target/release/dora-runtime